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IFormatProvider F# snippets (#7768)
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‎snippets/fsharp/System/IFormatProvider/Overview/Provider.fs

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module Provider
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// <Snippet2>
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open System
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open System.Globalization
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type AcctNumberFormat() =
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let [<Literal>] ACCT_LENGTH = 12
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interface IFormatProvider with
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member this.GetFormat(formatType: Type) =
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if formatType = typeof<ICustomFormatter> then
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this
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else
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null
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interface ICustomFormatter with
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member this.Format(fmt: string, arg: obj, formatProvider: IFormatProvider) =
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// Provide default formatting if arg is not an Int64.
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// Provide default formatting for unsupported format strings.
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let ufmt = fmt.ToUpper CultureInfo.InvariantCulture
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if arg.GetType() = typeof<Int64> && (ufmt = "H" || ufmt = "I") then
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// Convert argument to a string.
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let result = string arg
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let result =
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// If account number is less than 12 characters, pad with leading zeroes.
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if result.Length < ACCT_LENGTH then
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result.PadLeft(ACCT_LENGTH, '0')
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else result
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let result =
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// If account number is more than 12 characters, truncate to 12 characters.
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if result.Length > ACCT_LENGTH then
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result.Substring(0, ACCT_LENGTH)
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else result
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// Integer-only format.
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if ufmt = "I" then
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result
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// Add hyphens for H format specifier.
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else // Hyphenated format.
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result.Substring(0, 5) + "-" + result.Substring(5, 3) + "-" + result.Substring(8)
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else
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try
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this.HandleOtherFormats(fmt, arg)
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with :? FormatException as e ->
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raise (FormatException($"The format of '{fmt}' is invalid.", e))
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member _.HandleOtherFormats(format: string, arg: obj) =
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match arg with
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| :? IFormattable as arg ->
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arg.ToString(format, CultureInfo.CurrentCulture)
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| null ->
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string arg
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| _ ->
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String.Empty
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// </Snippet2>
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// <Snippet1>
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open System
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open System.Globalization
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type DaysOfWeek = Monday = 1 | Tuesday = 2
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[<EntryPoint>]
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let main _ =
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let acctNumber = 104254567890L
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let balance = 16.34
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let wday = DaysOfWeek.Monday
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let output =
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String.Format(AcctNumberFormat(),
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"On {2}, the balance of account {0:H} was {1:C2}.",
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acctNumber, balance, wday)
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printfn $"{output}"
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let wday = DaysOfWeek.Tuesday
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let output =
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String.Format(AcctNumberFormat(),
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"On {2}, the balance of account {0:I} was {1:C2}.",
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acctNumber, balance, wday)
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printfn $"{output}"
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0
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// The example displays the following output:
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// On Monday, the balance of account 10425-456-7890 was $16.34.
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// On Tuesday, the balance of account 104254567890 was $16.34.
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// </Snippet1>
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‎snippets/fsharp/System/IFormatProvider/Overview/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="provider2.fs" />
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<Compile Include="Provider.fs" />
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</ItemGroup>
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</Project>

‎snippets/fsharp/System/IFormatProvider/Overview/provider2.fs

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module provider2
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// <Snippet3>
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open System
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open System.Globalization
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let dateValue = DateTime(2009, 6, 1, 16, 37, 0)
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let cultures =
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[ CultureInfo "en-US"
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CultureInfo "fr-FR"
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CultureInfo "it-IT"
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CultureInfo "de-DE" ]
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for culture in cultures do
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printfn $"{culture.Name}: {dateValue.ToString culture}"
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// The example displays the following output:
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// en-US: 6/1/2009 4:37:00 PM
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// fr-FR: 01/06/2009 16:37:00
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// it-IT: 01/06/2009 16.37.00
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// de-DE: 01.06.2009 16:37:00
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// </Snippet3>

‎xml/System/IFormatProvider.xml

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The following example illustrates how an <xref:System.IFormatProvider> implementation can change the representation of a date and time value. In this case, a single date is displayed by using <xref:System.Globalization.CultureInfo> objects that represent four different cultures.
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:::code language="csharp" source="~/snippets/csharp/System/IFormatProvider/Overview/provider2.cs" interactive="try-dotnet" id="Snippet3":::
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:::code language="fsharp" source="~/snippets/fsharp/System/IFormatProvider/Overview/provider2.fs" id="Snippet3":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.IFormatProvider.Class/vb/provider2.vb" id="Snippet3":::
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The following example illustrates the use of a class that implements the <xref:System.IFormatProvider> interface and the <xref:System.IFormatProvider.GetFormat%2A> method. The `AcctNumberFormat` class converts an <xref:System.Int64> value that represents an account number to a formatted 12-digit account number. Its `GetFormat` method returns a reference to the current `AcctNumberFormat` instance if the `formatType` parameter refers to a class that implements <xref:System.ICustomFormatter>; otherwise, `GetFormat` returns `null`.
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:::code language="csharp" source="~/snippets/csharp/System/IFormatProvider/Overview/Provider.cs" id="Snippet2":::
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:::code language="fsharp" source="~/snippets/fsharp/System/IFormatProvider/Overview/Provider.fs" id="Snippet2":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.IFormatProvider.Class/vb/Provider.vb" id="Snippet2":::
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The class that implements <xref:System.IFormatProvider> can then be used in a call to a formatting and parsing operation. For example, the following code calls the <xref:System.String.Format%28System.IFormatProvider%2CSystem.String%2CSystem.Object%5B%5D%29?displayProperty=nameWithType> method to generate a string that contains a formatted 12-digit account number.
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:::code language="csharp" source="~/snippets/csharp/System/IFormatProvider/Overview/Provider.cs" id="Snippet1":::
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:::code language="fsharp" source="~/snippets/fsharp/System/IFormatProvider/Overview/Provider.fs" id="Snippet1":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.IFormatProvider.Class/vb/Provider.vb" id="Snippet1":::
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]]></format>
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The following example illustrates the use of a class that implements the <xref:System.IFormatProvider> interface and the <xref:System.IFormatProvider.GetFormat%2A> method. The `AcctNumberFormat` class converts an <xref:System.Int64> value that represents an account number to a formatted 12-digit account number. Its `GetFormat` method returns a reference to itself if the `formatType` parameter refers to a class that implements <xref:System.ICustomFormatter>; otherwise, `GetFormat` returns `null`.
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:::code language="csharp" source="~/snippets/csharp/System/IFormatProvider/Overview/Provider.cs" id="Snippet2":::
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:::code language="fsharp" source="~/snippets/fsharp/System/IFormatProvider/Overview/Provider.fs" id="Snippet2":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.IFormatProvider.Class/vb/Provider.vb" id="Snippet2":::
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An instance of the `AcctNumberFormat` class can then be passed as an argument to a method that provides formatting or parsing services. For example, the following code passes an `AcctNumberFormat` class to the <xref:System.String.Format%28System.IFormatProvider%2CSystem.String%2CSystem.Object%5B%5D%29?displayProperty=nameWithType> method to generate a formatted 12-digit account number.
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:::code language="csharp" source="~/snippets/csharp/System/IFormatProvider/Overview/Provider.cs" id="Snippet1":::
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:::code language="fsharp" source="~/snippets/fsharp/System/IFormatProvider/Overview/Provider.fs" id="Snippet1":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.IFormatProvider.Class/vb/Provider.vb" id="Snippet1":::
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]]></format>

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